The long-term objectives are to develop 17O magnetic resonance imaging (OMRI) and spectroscopy (OMRS) to a stage that 17O then may be used: 1) in physiological research and 2) for clinical diagnostic purposes. MRI may be very useful in studying physiological processes in which oxygen plays a major metabolic role. It can noninvasively measure the regional metabolic rate of oxygen (rMR02) and regional blood flow (rBF) in many body organs, particularly, brain. There is no radiation exposure. The specific aims of the current application are to develop the hardware and software for 170 MRI imaging in a whole body clinical imager and to test the method by: 1) using phantoms of water at physiological pH. 2) imaging the baboon brain, 3) imaging the human brain, 4) in-vivo measurements of brain pH 5) measuring cerebral metabolism rate of oxygen (CMRO2) and cerebral blood flow (CBF) in the baboon, 6) studying the effects of anesthetics on CMR02 and CBF in the baboon, and 7) measuring CMRO, and CBF in man. 17O MRI offers an additional means to conventional proton MRI of brain water. 17O MRI is more sensitive to slower molecular motions than 1H MRI. This may allow earlier diagnosis of tissue pathology. 17O nuclear relaxation times are two to three orders of magnitude shorter than 1H, opening the way to study faster bio-molecular physiological processes. The proposed methodology is unique in being noninvasive, in utilizing a stable (non-radioactive) isotope and in being carried out in-vivo utilizing conventional MRI scanners. 17O MRI methodology may have great potential for both physiological and pathophysiological studies in man and for improving our understanding of numerous disease processes including dementia, stroke, head trauma, cancer and epilepsy. Cerebral ischemia, dementia, pseudotumor cerebri and low grade brain tumors all of which are difficult to detect on conventional proton MRI, may be better delineated and studied. Tissue perfusion can be noninvasively measured in brain and other organs, perhaps providing a means to detect early microvascular changes characteristic of such diseases processes as diabetes mellitus and hypertension.